Now that Ignition has the dedicated TestTypeOf operator, there's not
really a point in doing the typeof with abstract/strict equal combining
in TurboFan anymore. In fact it's counter-productive to do so, as it
might try to cover typeof comparisons in cases where it's better to just
compute the typeof once, i.e.:

  let x = typeof a, y = typeof b;
  if (x === y) {
    if (x === 'string') {
      ...
    }
  }

Here we would combine the second comparison into an ObjectIsString, and
still compute the typeof a.

R=jarin@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2780953003
Cr-Commit-Position: refs/heads/master@{#44220}